The present invention relates to electronic devices, and, more particularly, to semiconductor memory circuits.
Memory Circuits
As is well known, digital computers use distal semiconductor primary memory and typically also have digital magnetic secondary memory. The primary memory stores current data and programs, and the secondary memory provides bulk storage. But other electronic systems also use memory in various ways. For example, in communication systems the use of frequency division multiplexing (FDM) to simultaneously broadcast differing information signals from several sources in a single locale requires a receiver be able to extract a desired information signal from a received broadband of simultaneous broadcasts. See schematic FIG. 1. Such extraction typically includes sampling of the received signal to form a digital signal (A/D converter 106) and then digital signal processing (digital down converter 108) to recover the desired information signal. The digital signal processing will use digital filtering following a mixing down (down conversion by the selected carrier frequency). The digital filtering often requires multiplications of filter coefficients with data samples, and typically the filter coefficients are stored in semiconductor read only memory (ROM) and the data samples temporarily stored in semiconductor random access memory (RAM). FIG. 2 illustrates a finite impulse response filter incorporating ROM 202 storing filter coefficients and dual port RAM 204 storing the data samples. These memories must be both fast due to high communication frequencies and low power duo to the portable nature of much communication systems.
Features
The present invention provides semiconductor memory with differential sensing and low capacitance layouts in both RAM and ROM for speed and low power.
It also provides self timed interface which allows memories to operate at optimum speed without requiring on chip glue logic to interface with the rest of a design.